Problem: $-\dfrac{5}{12} + \dfrac{9}{3} = {?}$
$ = - {\dfrac{5 \times 1}{12 \times 1}} + {\dfrac{9 \times 4}{3 \times 4}} $ $ = - {\dfrac{5}{12}} + {\dfrac{36}{12}} $ $ = - \dfrac{{5} + {36}}{12} $ $ = \dfrac{31}{12}$